For high breakdown voltage and low on-resistance of semiconductor devices, it is advantageous to use a material having high critical electric field. Nitride semiconductors have high critical electric field intensity. Thus, a semiconductor device achieving high breakdown voltage and low on-resistance is obtained by using such nitride semiconductors.
In a nitride semiconductor device, the electric field may concentrate at an edge of the gate electrode or an edge of the field plate electrode. This may hamper effective use of high withstand capability intrinsic to nitride semiconductors.